1. Field of the Invention
This invention relates to oil slurries of solid particulate carbonaceous material and more particularly to stabilized oil slurries of powdered coal or coke containing imidazoline quaternary salts as stabilizers.
2. Description of the Prior Art
Addition of solid particulate carbonaceous material, such as coal or coke, to a liquid hydrocarbon fuel, such as fuel oil, has been studied for many years. In the past five years, and particularly during the last two years, importance of reducing dependency of the world upon natural gas and liquid hydrocarbon fuels for its energy has been dramatically demonstrated.
Though not providing a complete solution to this energy problem, attempts have been made to incorporate solid particulate carbonaceous material, such as coal and coke, in liquid hydrocarbon fuels, because these particulate carbonaceous materials are far more plentiful than liquid fuels. There is considerable interest in extending and/or supplementing liquid fuels with solid fuels.
Many large industrial fuel users have equipment which was designed and constructed for the transportation, storage and combustion of liquid fuels. As yet, solid-liquid slurries, suspensions or emulsions are not accepted for regular use in such conventional equipment. In some instances this equipment was converted from its original design for burning solid fuels to liquid fuels. Many believe this trend should be reversed.
Various solutions to the problem of combining a solid particulate carbonaceous material with a liquid hydrocarbon fuel have been explored. One solution involved grinding carbonaceous material to colloidal size before introducing it into an oil. Even though this solution was successful, grinding costs were prohibitive. Coal oil slurries tend to form gels when heated to usable temperatures during storage, usually thixotropic gels.
Attempts were made to use the gelling phenomenon to hold larger than colloidal size particles in suspension. The gel was later broken down by adding additional oil so that the resulting slurry was pumpable without particulate material settling out. Inherently, this procedure was an expensive batch process.
Various materials were also added in an attempt to stabilize a coal oil slurry against settling of larger than colloidal size coal particles. Lime-rosin and starch were added to prevent settling of the larger slurry particles. Casein, gelatin and rubber were also added as suspension stabilizing agents to inhibit settling of coal particles. It was found that these suspension stabilizing agents must be added in quantities which undesirably thicken and increase viscosity of the slurry in order to prevent substantial quantities of coal particulate material from settling. Increasing slurry viscosity not only reduced the settling problem, but also limited uses to which the slurry may be put.
U.S. Pat. No. 4,069,022--Metzger, issued Jan. 17, 1978, describes a substantially water-free, high solid content, stable and combustible fuel slurry of about 5 to about 50 weight percent of a solid particulate carbonaceous material with the balance of the slurry being a liquid hydrocarbon fuel, a slurry suspension stabilizing agent and a water-free slurry viscosity reducing agent. The viscosity reducing agent was present in an amount sufficient to maintain the slurry at a viscosity below about 300 seconds Saybolt Universal when the slurry is at a temperature of 175.degree. F. Preferably, the viscosity reducing agent was a soap and the suspension stabilizing agent was starch.
The process for preventing formation of a gel in and controlling the settling and viscosity of this slurry involved the step of adding to the slurry containing a suspension stabilizing agent, a soap or salt of a fatty acid in an amount sufficient to maintain the viscosity of the slurry below 300 seconds Saybolt Universal when the slurry temperature was 175.degree. F.
U.S. Pat. No. 3,210,168--Morway, issued Oct. 5, 1965, describes a stabilized slurry of pulverized coal coated with a liquid hydrocarbon fuel in water to make the slurry pumpable through a pipeline. The slurry is stabilized with an imidazoline surfactant having the formula: ##STR1## where R is an aliphatic hydrocarbon chain radical containing from 10 to 23 carbon atoms.
U.S. Pat. No. 4,201,552--Rowell et al., issued May 6, 1980, describe coal oil slurries stabilized with certain cationic surfactants having the group EQU &gt;N--CH.sub.2 --CH.sub.2 --O--
where the group forms part of a straight chain such as Ethomeen.RTM. C-20 or cyclic ring such as N-soya-N-ethyl morpholinium ethosulfate.